Production of liquid hydrogen

The potential short-supply of petroleum-based fuels has led to activities by NASA to establish technical characteristics of air transportation systems that would use hydrogen-fueled aircraft. These activities cover sources and production of liquid hydrogen, aircraft configurations, and air terminal modifications, as affected by the introduction of liquid-hydrogen-fueled aircraft. ... 

The significant liquefaction yields that are presumed to have been derived from some macrinite-rich samples may attest to a contribution to conversion from this maceral. However, results from durains, and splint and cannel coals, which may contain large amounts of macrinite, generally have been variable (50). The conversion which we achieved with a coal containing 21% macrinite indicated that there was a contribution to the liquid products of batch hydrogenation from this maceral. Further, the residues examined from runs made with this coal at a series of temperatures contained no distinguishable macrinite product once a temperature of 425°C had been reached (66). 

A schematic diagram of the liquid solvent extraction process is illustrated in Figure 1. Where the production of liquid hydrocarbons is the main objective an hydrogenated donor process solvent is used, whereas in the production of needle coke this is not necessary and a coal derived high boiling aromatic solvent may be used (e.g. anthracene oil). An essential economic requirement of the process is that a high extraction yield of the coal is obtained and this will depend upon the coal used and the digestion conditions. 

We have divided the discussion into three principal areas. The first two sections deal with the production of atomic hydrogen species in gaseous and liquid environments the third is really a collage of experimental observations and unintentional introduction techniques that are generally of less interest from the viewpoint of a manufacturing technologist. 

However, it has to be noted that, from the perspective of providing mobility, by using that natural gas as feedstock -and taking into account fuel production and vehicle conversion efficiencies - the majority of passenger cars can be fuelled with the production of liquid fuels from oil sands, followed (with about a factor of three less) by its conversion into hydrogen and subsequent use in fuel-cell vehicles, and its direct use in CNG vehicles. 

Fischer-Tropsch (FT) synthesis is a catalysed chemical reaction in which carbon monoxide (CO) and hydrogen (H2) are converted into liquid hydrocarbons of various forms. Typical catalysts used are based on iron (Fe) and cobalt (Co). The production of liquid hydrocarbons using FT synthesis is a well known process. It was invented by Franz Fischer and Hans Tropsch in the 1920s in Germany. It follows the reaction ... 

A modification of the pyrolysis process, developed by Hoppe-Seyler in 1871, involved the addition of water and alkali to biomass which was converted into oil, gas, water-soluble components, and carbonaceous material. " The addition of carbon monoxide and hydrogen in the liquefaction process allowed the production of liquid fuels from biomass. Asphalt substitutes have also been prepared from biomass under liquefaction conditions. ... 

The foregoing observations have direct implications to coal structure. In the present work, the production of liquids is facile below about 15% liquids yield and requires little hydrogen consumption. The processes most probably involve the release of species which are physically trapped or are weakly bonded to the insoluble matrix. At high conversions, the products are derived from the breakdown of the macromolecular network. This phase of conversion requires the cleavage and stabilisation of strong bonds, thereby creating an appreciable demand for hydrogen. 

The available information leads one to believe that the maximum production of liquids with no net hydrogen consumption and the low-temperature catalytic hydrocarbonization/gasification are alternatives which appear to have great merit. The former of these, when applied to western coals, appears to be technically ready for commercial application and economically competitive with alternative coal liquefaction processes. Advantages of the flash hydropyrolysis processes over the Coalcon process are difficult to perceive. 

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